Need help with dinos

[Amritansh]

I think these are large cell amphidinium, but not sure.
1st year of reef tank keeping (tank is about 10 month old)
Evo 13.5
Parameters as of latest reading and (ranges over 4 weeks)
Salinity 35.0 ranges (34.7-35.1)
Nitrate 6 ppm (9.8 - 6) reducing over time since I added skimmer
Phosphate - 0.01 ppm (0.02 - 0.01)
Calcium 450 (410-450)
Magnesium 1320 (1290 - 1350)
Alkalinity 10.9 (8.0 - 10.9) has been steadily increasing as i started dosing all for reef
PH 8.1 (8 - 8.1)

I do weekly 10% water change
Also add reef energy ab+ once a week
There are zoas, Xenia, GSP, hammer, frogspawn, chalice, galaxea corals and all are doing well. The zoa are getting new heads more frequently lately.

The dinos disappear at night, and are most prominent after lights have been on a while. They don't really seem to have strands or much slime.
They also seem to only be on the sand, the rocks seem to not have any.

 

[Amritansh]

Adding a video in case it helps

 

[The Mushroom Man]

Hi Amritansh, i would raise phosphates a bit to around 0.08 or 0.10 add something like Microbacter 7 or beneficial bacteria, Are you running a UV highly recommended to get one of those if not already, last ditch effort would to wrap the tank and go lights out for 2-3 days change all filter media then do a 25-40% water change. Good luck